Electrecaiu stethoscope



Sept. 18, 1945 B. 'MINSKY ELECTRICAL STETHOSCOPE Filed March 4; 1944 2 Sheets-Sheet 1 INVEZN'TEIR p 1945- B. MINSKY 2,385,221

ELECTRICAL STETI' IOSGOPE I Filed March 4, 19.44 2 Sheets-Sheet 2 IIIIIIIIIIIIIIIIIIIIIIIIIIAQ 1,.

INVENTUR= M,&JM+ BH Patented Sept. 18, 1945 s PATENT '2 OFFICE smcmc'aa s'rs'rnoscors Benjamin Minsky, Allston, Masa, assignor of two-thirds to Aaron Minsky, Allston, Mass.

Application March 4,1944, Serial No. 525,053, 4 Claims. (6i. 1181-24) This invention relates to lectrical stethoscopes and more particularly to an electrical stethoscope of the portable type.

It is the primary aim and object of the present invention to devise an electrical stethoscopewhich has as nearly as possible the characteristic appearance of, and is of approximately the same light weight as, the conventional air conductor type stethoscope used for general auscultative examination.

It is a more specific object of the present in vention to construct the electrical stethoscope so that electrical units thereof may be separately detached for a check, repair or replacement.

- It is also among the objects of the present invention electrically to transmit the sounds picked up from their inception by the stethoscope substantially to the ears of the physician using the stethoscope.

The foregoing and other objects of the invention, together with means whereby the latter may be carried into effect will best be understood from the following description of an illustrative embodiment shown in the accompanying drawings: in which,

Fig. 1 is a front elevation of an electrical stethoscope embodying the present invention.

' Fig. 2 is a side elevation of the same stethoscope.

Fig. 3 is a wiring diagram of an amplifier which may be used in the present stethoscope.

Fig. 4 is a greatly enlarged fragmentary section taken on the line 44 of Fig. 2.

Fig. 5 is a section taken on the line 5-5 of Fig. 4.

Fig. 6 is a fragmentary front elevation, partly in section, of an electrical stethoscope embodying the present. invention in a modified form.

Referring to Figs. 1 and 2 of the drawings, the

reference numeral ll) denotes a pair of conventional ear tubes which are yieldingly connected by a bent leaf spring 12. Mounted on the upper; end ll of each tube 10 is an ear phone IE (to be described hereinafter) having -a projecting ear piece 18. A strap I9 of any suitable flexible material such as leather, for instance, connects the lower ends of the ear tubes I0 and prevents approach of the ear phones IG'at the upper ends of the ear tubes beyond the relative disposition shown in Fig. 1. A frame is suspended from the lower ends of the ear tubes 10 by straps 22 in the manner indicated in Figs. 1 and 2. The straps 22 are preferably of a non-metallic flexible material such as leather, for instance. The frame 20 is in the present instance U-shaped in front elevation (Fig. 1), and has preferably an integral back wall 23 to lend added rigidity to the frame. Suitably mounted in the parallel legs 28 of the frame 20 are aligned bearings 25 which are preferably non-wearing jewel bearings. Journalled in the bearings 25 of the frame 20 are studs 26 on-a casing 21 which is open at the top. Recelved in the casing 21 is an amplifier unit 28 (to be described hereinafter). The back wall 29 of the casing 21 preferably extends upwardly to the top of the amplifier unit 28, while the side walls 30 and the front wall 3| of said casing do not reach to the top of the amplifier unit so as to expose certain control knobs 32, 33 and 34 on the latter. The amplifier unit 28 is slidable into the casing 21 from the top thereof and-may be as readily removed therefrom. Mounted on the bottom wall 35 oi the casing 21 is the male member 36 of a conventional two-prong shielded cable go connector 31 whose cooperating female member (not shown) is retractible from the male member 36 and mounted in the amplifier unit '28. The cable connector 31 forms part of the electrical connection between the amplifier unit 28 and a 25 special type of piezo-electric microphone 38 used for general auscultative examinations and known to the trade as "stethophone." Thus, the microphone 38 is electrically connected with the amplifier unit 28 when the latter is in the casing 21 and the members of. the cable connector 31 engaged, and the microphone is disconnected'from the amplifier unit by the simple expediency of removing the latter from its casing 21 and thereby withdrawing the female member of the connector 31 from the male member 36 thereof. The male member 36 of the connector 31 has a shank 38 which extends to the outside of the casing 21 and is preferably shaped as shown in Fig. 1 to securely receive one end of a flexible tube 40 on which the microphone. is suspended and which is preferably of rubber. A shielded electric cable 41 whose wires connect the microphone 38 with the male member 35 of the connector 31, preferably. extends through the suspension tube II which may be provided with an internal wire sheath 42 to serve as an additional shield for the cable 41.

The electrical connections between the amplifier unit 28 and the ear phones 16 include shielded electric cables 45 and which preferably pass through the ear tubes It and are connected with the male member 41 of aconventional, shielded multi-prong cable connector 48 whose cooperating female member (not shown) i mounted in the amplifier unit 28. The male member 41 of the connector 48 is retractible from the female member thereof and, when engaged with the latter, extends through an aperture 49' On removal of'the male member 41 of the connector 48 from the female member thereof, the electrical connection between the ear phones I6 and the amplifier unit 28 is interrupted and the latter may be removed from its casing 21 without any obstruction from the male member 41 of the connector 48, as will be readily understood.

A source of electric power in the form of an "A" battery and a B battery (neither shown in Figs. 1 and 2) is connected with the amplifier unit 28 through an electric cable 55 and a conventional multi-prong cable connector 56 whose male member 51 is directly connected with the wires of the cable 55 and retractible from the cooperating female member thereof. The A and B batteries may be conveniently carried in a suitable case (not shown) strapped to the users belt, for instance.

The amplifier unit 28, comprises a housing 68 (Figs. 1 and 2) for the chassis (not shown) on which the electrical components of the amplifier are mounted. Since numerous standardized circuits may be used for the amplifier and since the amplifier circuit does not form a part of the present invention, I do not limit the use of the present stethoscope with an amplifier of any particular circuit. A circuit which may be-used for the amplifier is, by way of example, shown in Fig. 3. In this circuit, the piezo-electric microphone 38 is shown connected to the grid of the first or input stage which consists of a high gain, high impedance, audio-frequency amplifier in the form of a pentode tube 6|. The second or intermediate stage consists of another pentode interstage audio-frequency amplifier 62. The third or output stage consists of an audio-frequency power output amplifier tube 63. These tubes 8| to 63 may be operated either as a resistancecapacity coupled, or a transformer-coupled, audio voltage amplifier unit operated according to either of the well-known classes "A, B or "AB. The A and B batteries 6 4 and 55 constitute the direct current source for the unit. In the present instance, the filaments 56 of the input and output tubes iii and 63 are connected in series, whereas the filament 61 of the interstage tube 62 is connected in parallel with the filaments E6 of the other tubes 64 and 63. The circuit shown in Fig. 3 operates according to class A with a single-ended output arrangement. The components of the first two stages further comprise condensers CI to C4, inclusive, and resistors Rl to R6, inclusive. and the components of the output stage further comprise a condenser C5=,-'a'plate choke CH, a bias cell BC, a main switch SW which is operated by the control knob 33 (Fig. 1), 'and'a volume control R1 which is operated by the control knob 32 (Fig. 1). Also included in the circuit, but not shown in Fig. 3, may be a conventional frequency-response filter which would be used to limit the amplifier from full response to a predetermined cut-off level. The filter would preferably be operated by the Since the ear phones I8 are identical in con-- struction, only one will be described in detail with special reference to Fig. 4. Each ear phone comprises a body 18 of any suitable insulating material in which is pressfitted or otherwise secured an internally threaded, metallic sleeve H which is screwed over the adjacent threaded end of one of the ear tubes In. Mounted in a cavity 12 in the body 18 is a diaphragm 13. Behind this diaphragm is a core 14 which is mounted in the body 10 and is of a material which holds no residual magnetism. Surrounding the core 14 is a solenoid coil 16 the ends of which are suitably connected with concentrically arranged contacts 11 and 18 (see also Fig. 5). These contacts are mounted on an insulating terminal disc 19 which is suitably secured in the sleeve 1|. Cooperating with the contacts 11 and 18 are similarly arranged contacts and 8|, respectively, which are mounted on an insulating terminal disc 82 suitably secured in the adjacent end of the ear tube 10- on which the earphone is screwed. The contacts 80 and BI. are connected with the wires 83 and 84 of the cable 46, for instance (Figs. 1 and 4), which passes through the ear tube It! to the amplifier unit 28. Suitably mounted on the body 10 of the earphone is an insulating cover 85 which closes the cavity 12 and carries a metal tip 86 over which an ear piece 18 is snapped in place. The tip 86 and ear piec 18 are provided with sound-conducting bores 81 and 88, respectively. It is evident from the preceding description that the earphones l6 may be readily removed from their respective ear tubes I0 for a check, repair or replacementrby simply unscrewing them from the latter, and that the .phone 38 and a few cables leading to the amplifier constitute the only noticeable departure in the appearance of the present stethoscope from that of a conventional air-conductor type stethoscope. The weight and size of the present stethoscope may readily be made to resemble that of a conventional air conductor type stethoscope, the amplifier unit being made small in size and of light weight. The technique involved in the professional use of the present instrument does not in the slightest deviate from that involved in the professional use of the conventional airconductor type stethoscope. For the foregoing reasons, the present instrument appeals greatly to the physician not only because it fills an urgent need of the medical profession for a stethoscope having greatly improved acoustic performance, but also because it is in its application, appearance, weight and size so much like the highly developed air-conductor type stethoscope to which every physician is used. The separate removability of various electrical units from the present instrument not only facilitates the initial assembly of the latter but also a check, repair or replacement of these electrical units.

While in the stethoscope shown in Figs. 1 and 2 the amplifier unit is removably carried in a special casing 21, the amplifier unit 94 of the stethoscope shown in Fig. 6 is directly carried by- 2,385,221' the frame 95 which may be suspended from the I ear tubes in the same fashion as the frame 29 in Fig. 1. To this end, the amplifier unit 9| is provided with opposite studs 98 which are received in ball-shaped bearings 91, preferably jewel bearings, which swivel in ball-shaped sockets 98 in bearing brackets 99. vA- retainer plate I holds each bearing 91 in its socket 99, and

each bearing bracket 99 has a drilled hole IIiI through which lubricant is conducted to its hearing. One of the bearing brackets 99 is firmly mounted on the frame 95 and the other bearing bracket, to wit 99, is integral with an arm I02 which is pivoted at I93 to the frame 95. The bearing bracket 99' is provided with a depression Hi4 with which normally registers a detent I95 on one end of a leaf spring I06, the other end of which is spotwelded on, or otherwise secured to, the frame 95. The detent I extends through a hole I91 in the frame 95 and is normally urged by the spring I06 into the depression I04 in the bearing bracket 99'. thereby locking the latter in place on the frame 95. To remove the amplifier unit 94 from the frame 95 for a check, repair or replacement, the free end of the leaf spring I06 is manipulated to cause withdrawal of the detent I95 from the depression I94, whereupon the arm I92 with the bearing bracket 99 is swung outwardly from the frame 95 until the swivel bearing 91 in the bearing bracket 99' clears the stud 96 which it bore. The amplifier unit 94 is thereupon removed from the fixed bearing 99. To mount the amplifier unit in the frame 95 is equally simple and requires no further description.

The "stethophone to be used with the instrument shown in Fig. 6 is removably suspended from the amplifier unit 94 by means of a flexible rubber tube iIIl and an electrical connector III whose members H2 and* H3 are metallic, and. hence, conductive. mounted on the male member 2 of the connector I II in the manner shown in Fig. 6, and the female member I I3 of said connector threadedly receives said male member H2 and is mounted on the bottom wall H4 of the amplifier casing II5 by a nut H6 which is screwed on said member II 3 and draws an annular shoulder IN on the latter into firm engagement with said bottom wall Ill of the amplifier casing. Leading from the microphone (not shown) are a signal conductor H8 and a shield H9, both of which preferably pass through the suspension tube I III. The signal conductor I I8 extends through an insulating terminal disc I20 in the connector member H2 and terminates in a contact point I'll, while the shield H9 is connected with the con- The suspension tube II 9 is nector member H2. The grid wire I22 of the first stage of the amplifier extends through an insulating terminal disc I23 and terminates in a contact point I24 which engages the contact point I2I when the connector members H2 and H2 are connected. A wire I25, which leads from the filament of the first tube of the amplifier, is

connected with the male member H3 of the conphone, a piezo-electric microphone, a flexible hose by which said microphone is suspended from said casing, and electrical connections passing through said ear tubes and hose, respectively, and

connecting said amplifier with saidear phones, and microphone, respectively.

2. The combination in an electrical stethoscope as set forth in claim 1, in which said amplifier is removably carried in said frame, and each of said connections includes separable electrical connectors.

3. In an electrical stethoscope, the combination of yieldingly connected ear tubes, a frame, non-metallic fiexible straps by which said frame is suspended from one end of said ear tubes. an ear phone mounted on the other end of each ear tube, an ear piece projecting from each ear phone, an open casing swivelled on said frame, an amplifier removably carried in said casing, a piezo-electric microphone, a flexible hose by which said microphone is suspended from said casing, and electrical connections passing through said ear tubes and hose, respectively, and connecting said amplifier with said ear phones and microphone, respectively.

4. In an electrical stethoscope, the combination of yieldingly connected ear tubes, a frame, non-metallic flexible straps by which said frame is suspended from one end of said ear tubes, an ear phone mounted on the other end of each ear tube, an ear piece projecting from each ear phone, an amplifier removably swivelled on said frame, a piezo-electric microphone, a flexible hose by which said microphone is suspended from said amplifier, and electrical connections passing through said ear tubes andhose, respectively, and connecting said amplifier with said ear phones and microphone, respectively.

BENJAMIN LUNSKY. 

